Effects of ascorbic acid and embryogenic microspore selection on embryogenesis in white cabbage (Brassica oleracea L. var. capitata)

Microspore embryogenesis in plants is a process by which microspores can switch their developmental pathway from gametophytic to embryogenic via specific inductive stress treatments, which results in the formation of haploid embryos. However, only a small portion of the cultured cells can undergo the entire process to produce embryos, and most die at different developmental stages during culture. The objective of this study was to improve the induction of embryogenesis in an isolated microspore culture (IMC) of white cabbage (Brassica oleracea L. var. capitata) by focussing on the regulation of dead microspores. The results indicated that microspores died rapidly after 24 h at a heat shock temperature of 32.5 degrees C, and that 80 - 90% were dead after 3 d in culture. Cell purification performed after 3 d in culture, eliminated most of the dead microspores and had a beneficial effect on embryo yield. Similarly, ascorbic acid (AsA) had a positive effect on the number of embryos produced by decreasing the mortality of microspores. A combination of 20 mg l(-1) AsA and cell purification after 3 d in culture significantly enhanced the efficiency of microspore embryogenesis, especially in the genotype 'Meiweizaosheng', in which embryo yields increased approx. 70-fold. Using this protocol, microspore viability and the initial rate of cell division were increased, which enabled more of the dividing microspores to develop further into complete embryos.